1. Field of the Invention
The present invention relates to improvements in lighting control systems of the type which automatically adjust the level of lighting in a room or the like based on predetermined needs of the user.
2. The Prior Art
Various lighting control systems have been devised and commercialized which automatically adjust the level of artificial lighting in a room to minimize energy consumption while satisfying the lighting needs of the occupant or room user. Such systems often comprise, for example, an occupant sensor, such as a conventional passive infrared or Doppler device, which operates to produce a control signal for a predetermined time interval after sensing the presence of a room occupant. Typically, a lighting control circuit responds to an interruption of this control signal to turn the room lighting off, thereby conserving energy when the room is determined by the sensor to be unoccupied. Such energy-saving lighting control systems may also include a photosensor which operates to produce an analog control signal based on the level of natural (daylight) lighting in the room. In response to this signal, the lighting control circuit adjusts the level of artificial light (e.g., as provided by fluorescent and/or incandescent lamps) such that the combination of natural and artificial light meets the needs of the user.
In addition to an occupant sensor and/or a photosensor, conventional energy-saving lighting control systems commonly include a dimming system by which the light level in a room can be manually adjusted. Such a dimming system comprises a manually movable actuator, such as a slider or a rotatable knob, which operates to adjust a potentiometer setting and thereby vary a lighting control signal based on its physical position.
In conventional systems of the above type, logic circuitry determines which of the various control signals has priority in controlling the brightness of the lamps. Generally, the controlling algorithm is that the control signal requiring the least light level has priority. Thus, should the control signal provided by the manually movable actuator require 50% lamp brightness while the occupant sensor control signal requires 0% lamp brightness (indicating that the room is unoccupied), the logic circuit will normally set the lamp brightness at zero. Similarly, if the room is occupied and the photosensor output requires 80% lamp brightness while the manually movable actuator is set for 60%, the logic circuit will set the lamp brightness at 60%, assuming an occupant sensor, if used, requires no less than 60% lamp brightness. Lighting control systems of this type are sold, for example, by Lithonia Control Systems under the trademark Equinox, and by Honeywell, Model EL 7305A1010, Electronic Ballast Controller.
Heretofore, decision-making in the energy-saving lighting control systems of the prior art has been achieved by logic circuitry comprising discrete operational amplifiers and impedance elements. Not being programmable, such circuitry has little flexibility in the features it offers. For example, there is no easy way to precisely adjust the maximum and minimum levels to which the lighting can be set; such circuitry usually operates to adjust the light level between full ON or full OFF. This is disadvantageous when a user desires to always have some minimum light level in an unoccupied room or hallway, or desires to operate the room lights at less than full power to conserve energy and prolong lamp life. Also, the normal output of such control circuitry cannot be readily overridden to satisfy certain unusual or off-normal needs of the user. When, for example, the system is designed to turn off the lights in response to a signal from the occupant sensor indicating an unoccupied room, one who desires to turn on the lights in the unoccupied room by a wall box control would first have to be detected by the occupant sensor. Only after detecting a user's presence will the occupant sensor allow the room light to be controlled by a wall-box control. This can be especially annoying, for example, to maintenance and security personnel who may want to quickly check the status of a room by reaching into the room from outside and moving the wallbox mounted dimmer actuator. Often, the occupant sensor is incapable of detecting such a small signal or, if it can, it may not be capable of "seeing" all entrances from which the room lighting can be controlled by a wall control.
Further disadvantages of conventional energy-saving lighting control systems are: (1) they are not designed to respond to an "emergency ON" signal, as may be produced by a fire or security system; (2) they do not respond to a "load shed" signal indicating that lighting power consumption should be reduced, such as during periods of peak demand for electrical power companies; (3) they have no means for easily and conveniently calibrating the photosensor output; and (4) their outputs cannot control different types of fluorescent ballasts.